The present invention relates to methods, compositions and devices for chemical balancing of chlorinated water, and more particularly, to methods compositions and devices of modulating the level of amide-containing chemicals such as cyanuric acid in chlorinated water of swimming pools, spas and similar water reservoirs.
Artificial swimming pools are known to have been built by the ancient Greeks and Romans who used them for athletic training in the palestras as well as for nautical games and military exercises. Roman emperors had private swimming pools in which fish also were kept, whence the Latin word for pool, piscina. In modern days, open air swimming pools represent a major worldwide attraction for children and adults all over the world as a recreational pastime, as providing the means for one of the most beneficial forms of exercise and as serving one of the major national and Olympic sports. The ever growing number of swimming pools is estimated to be in excess of 20 millions pools worldwide. Preserving the water quality of these pools is a major health and aesthetic concern and the source of an industry and business of several hundreds of millions of US dollars a year.
Maintaining the water quality in swimming pools, spas, hot-tubs, waterslides, and other circulating reservoirs for sports, recreational, therapeutic and ceremonial bathing, as well as decorative landscaping structures such as fountains and pools, presents a considerable challenge in which a critical balance has to be preserved between the various oxidizers, sanitizers, clarifiers, conditioners, disinfectants and the likes that are added to the pool or are formed therein. The life time in the pool water of most chemicals, is limited by their chemical and/or photochemical degradation, evaporation and/or removal by filtration, backwashing, drainage, spillage and sedimentation.
“Free chlorine”, a phrase which is used herein to describe Cl+, is a highly effective antimicrobial agent, which has a wide biocidal activity (e.g., antibacterial, antifungal, antialgal and antiviral activities). It is routinely used in water treatment systems. Hypochlorous acid, HOCl, is a common source of free chlorine, via the hypochlorite ion OCl− (see, scheme 1 below), and is typically used as an aggressive oxidizing and chlorinating agent for various applications, including water purification systems.

The mechanism of the biocidic action exerted by free chlorine-producing agents, such as sodium hypochlorite and hypochlorous acid, is not fully understood. It is assumed that free chlorine is responsible for the oxidation reactions with the cytoplasm of microorganisms (e.g., bacteria, vegetative bacteria, algae, spore, virus, or fungus), after diffusion through the cell walls. Hypochlorous acid penetrates the cell walls readily due to its size, structure and neutrality, which are similar to that of water. Once present in the cell, chlorine disturbs the production of ATP (adenosine triphosphate), an essential compound for the respiration of microorganisms, as well as the structure and thus activity of polynucleic acids, which are essential for all cell functions and reproduction.
Direct use of chlorine gas and/or HOCl is limited due to their high reactivity and aggressiveness as oxidizing agents. Hence, the use of compounds that are capable of releasing HOCl and thus act as indirect oxidizing agents is preferred.
Chemical compounds which release a halogen disinfectant agent when coming in contact with water, primarily free chlorine donor biocides, are the major and most commonly used sanitizers in swimming pools. These sanitizers ensure that the water in the swimming pool remains clean and safe for the swimmers throughout the day. However, hypochlorous acid is highly unstable, and readily decomposes into inactive breakdown products, such as hydrochloric acid, water and oxygen, via UV radiation driven photochemical reactions upon exposure to direct sun light, and/or upon exposure to moderate and high temperatures. During the summer, which is the peak season for swimming pools, up to 90% of the total active chlorine species are lost in a sunny day over two to three hours. In order to control these effects and preserve the effectiveness of the chlorine, agents aimed at stabilizing the chlorine are often added to the water.
The most commonly used and effective chlorine stabilizer is cyanuric acid, also known by its tautomer's name, s-triazinetrione or isocyanuric acid (see, Scheme 2 below).

Cyanuric acid, as well as cyanurate salts and various derivatives thereof are compounds which protect the chlorine from the negative effects of UV and heat, and therefore practically reduce the amount of chlorine which needs to be added to the water in order to maintain safe conditions of disinfection. The protection action of these compounds is achieved by the ability of free chlorine, Cl+, to reversibly bind to the nitrogen atoms in the cyanuric acid ring, as depicted in Scheme 3 below.

This relatively slow equilibrium keeps some of the hypochlorous acid in this bound form, thus protecting it from photochemical decomposition as long as the Cl+ is bound to the triazine ring.
Hence, cyanuric acid, as well as cyanurate salts and various derivatives thereof, are commonly added to most commercially available chlorine tablets, or used as a separate chemical in addition to active-chlorine generating compounds.
With a correct dosing, cyanuric acid can reduce the chlorine consumption during the sunny season. Pool water treated with 25 to 50 milligrams per liter of cyanuric acid loses only 10 to 15 percent of their total chlorine as compared to untreated water under the same conditions. However, incorrect balance of cyanuric acid can create an over-protective effect and hence substantially decrease the effectiveness of chlorine as a disinfectant.
More common are sanitizing chemicals which are based on N-halogenated cyanurate compounds such as trichlorocyanuric acid (TCCA, trichloro-s-triazinetrione or 1,3,5-trichloro-[1,3,5]triazinane-2,4,6-trione; see, Scheme 3 above), halogenated hydantoins such as 1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH), 1,3-dichloro-5,5-dimethylhydantion (DCDMH), and 1,3-dichloro-5-ethyl-5-methylhydantoin, halogenated melamines such as N,N,N-trichloromelamine, and halogenated glycolurils such as N,N,N,N-tetrachloroglycoluril, salts thereof for faster dissolution in water, and combinations thereof. Such compounds have dual effect: release of active chlorine species and controlling the level of chlorine species in water.
Due to gradual and unavoidable degradation of hypochlorous acid in the water, routine addition of these commonly used stabilized chlorine-based sanitizers mentioned above, such as trichloroisocyanuric acid (trichloro-s-triazinetrione) or its faster dissolving sodium dichloroisocyanurate (sodium dichloro-s-triazinetrione), bring about a gradual rise in cyanuric acid concentration in the pool's water. An ideal cyanuric acid level, suitable for public swimming pools and spas, should be maintained at about 50 ppm (parts per million), with an acceptable range of 30 to 70 ppm. To achieve 50 ppm of cyanuric acid, 2 kilograms of the stabilizer must be added to 40 cubic meters (m3) of chlorinated pool water.
Excessive amounts of cyanuric acid drive the equilibrium, depicted in Scheme 3 above, towards the uptake of free chlorine. Hence, excessive amounts of cyanuric acid cause the chlorine to become progressively over-stabilized and interfere with its disinfection function. The phenomenon known as “chlorine-lock” takes place when the concentration of cyanuric acid reaches over 100 ppm (0.77 mM). Chlorine-lock expresses itself similarly to inadequately low chlorine level, in clouding of the pool's water which, apart from an aesthetic nuisance, is a clear indication that the water is no longer safe for use.
Once added to the pool, cyanuric acid does not dissipate or degrade substantially. It is removed from the pool only by splash-out and backwash waste procedures or dilution. Typically, cyanuric acid level is lowered by draining part of the pool's water and diluting the remaining water with fresh water. If the cyanuric acid level exceeds 100 ppm considerably, the pool ought to be partially or totally drained and have its inner-walls scrubbed (cyanuric acid will sediment on the sides of the pool). This time-consuming and water-wasteful process is extremely costly not only in terms of water but also in lost of pool's operational time, additional stabilized chlorine added, and the so far unavoidable reiterative nature of the overall process needed to maintain the balance between the concentration of reactive chlorine species and the concentration of cyanuric acid.
Reservoir water, including water of swimming pools and spas, is typically treated in closed or semi-closed systems which circulate the water through a water treatment plant comprising filters and other devices for monitoring and adjusting the chemical balance of the water.
Filters of various mesh size remove particulates from the water without changing the chemical composition of the water in terms of dissolved chemicals. Other devices such as ion exchange columns, typically used to adjust the pH of the water and to remove salts and other dissolved chemicals, and erosion chemical feed systems, also known as erosion feeders which are typically used to gradually add chemicals to the water, are responsible for adjusting the chemical composition of the water.
Water filtration, treatment and purification devices are disclosed for example, in U.S. Pat. Nos. 3,957,617, 4,412,919, 4,969,996, 5,108,606, 5,336,398, 5,688,588, 6,627,073, 6,649,045, 6,887,379 and 6,932,889. The main concept of these water treatment devices is passing pre-treated water through a device which comprises a container filled with an insoluble solid granulose matrix. This matrix, once packed in the container, remains penetrable to water by virtue of channels and interconnected cavities in and between the matrix granules, having a predetermined maximal mesh size, which effects the filtration, purification and treatment of the water by absorbing or otherwise eliminating undesired substances in the water entering the device, and in some cases adding desired substances to the water exiting the device.
Other methods for treatment of water include physicochemical means such as irradiation with biocidic radiation such as UV or gamma, heating, distillation, subjection to magnetic and/or electric fields, vortices and centrifugation, and the likes.
Recently, a new approach for chemical adjustment of pool water has employed biochemical catalysts, namely enzymes. U.S. Pat. No. 6,372,472 teaches filter media containing powdered cellulose and immobilized lipase for swimming pool and spa water filtration and treatment. This filtering media absorbs oils contained in pool or spa water, and the lipase hydrolyzes the oils, thus ridding the water of a major and common esthetic nuisance.
Immobilization of proteins, including enzymes, while retaining the biochemical activity thereof, on solid support of various materials, is disclosed in numerous publications such as U.S. Pat. Nos. 4,071,409, 4,090,919, 4,258,133, 4,888,285, 5,177,013, 5,998,183, 6,905,733, and 6,987,079, U.S. Patent Application No. 2003/0096383, and other publications such as Yan A-X. et al., 2002, Applied Biochemistry and Biotechnology, Vol. 101(2), pp. 113-130(18); and Ye, Yun-hua et al., 2004, Peptide Science, Vol. 41, pp 613-616.
None of these methods and devices, however, effects the removal or otherwise lowering cyanuric acid levels in water reservoirs, such as pools or spas. As discussed hereinabove, to date, removal of cyanuric acid involves time and cost consuming actions such as draining the water reservoir.
There is thus a widely recognized need for, and it would be highly advantageous to have methods and devices which can modulate the levels of cyanuric acid in water, devoid of the above limitations.